7SR210 & 7SR220 Description of Operation
Unrestricted ©2018 Siemens Protection Devices Limited
Page 47 of 94
3.11 Current Protection: Thermal Overload (49)
The relay provides a thermal overload suitable for the protection of static plant. Phase segregated elements are
provided. The temperature of the protected equipment is not measured directly. Instead, thermal overload
conditions are calculated using the measure True RMS current.
Should the current rise above the
49 Overload Setting
for a defined time an output signal will be initiated.
Operate Time (t): -
Where
T = Time in minutes
t
=
49 Time Constant
setting (minutes)
In = Log Natural
I = measured current
I
P
= Previous steady state current level
k = Constant
I
B
= Basic current, typically the same as In
k.I
B
=
49 Overload
Setting (I
q
)
Additionally, an alarm can be given if the thermal state of the system exceeds a specified percentage of the
protected equipment’s thermal capacity
49 Capacity Alarm
setting.
For the heating curve: -
Where:
q
= thermal state at time t
I = measured thermal current
I
q
=
49 Overload
setting (or k.I
B
)
The final steady state thermal condition can be predicted for any steady state value of input current where t >
t
,
Where:
q
F
= final thermal state before disconnection of device
49 Overload Setting
I
q
is expressed as a multiple of the relay nominal current and is equivalent to the factor k.I
B
as defined in the IEC255-8 thermal operating characteristics. It is the value of current above which 100% of
thermal capacity will be reached after a period of time and it is therefore normally set slightly above the full load
current of the protected device.
The thermal state may be reset from the fascia or externally via a binary input.
Thermal overload protection can be inhibited from: -
Inhibit 49
A binary or virtual input, function key or remote data Comms.
(
)
þ
ý
ü
î
í
ì
´
-
-
´
=
2
B
2
2
P
2
I
k
I
I
I
ln
t
t
100%
)
e
(1
I
I
θ
τ
t
2
θ
2
´
-
×
=
-
100%
I
I
θ
2
θ
2
F
´
=
Summary of Contents for Argus 7SR21
Page 1: ...Energy Management 7SR21 7SR22 Argus Overcurrent Relay Reyrolle Protection Devices ...
Page 2: ......
Page 4: ...Contents 7SR11 and 7SR12 Page 2 of 2 2018 Siemens Protection Devices Limited ...
Page 185: ...7SR210 Settings Guide Unrestricted 2018 Siemens Protection Devices Limited Page 61 of 61 ...
Page 277: ...7SR220 Settings Guide Unrestricted Page 72 of 107 2013 Siemens Protection Devices Limited ...
Page 382: ...7SR220 Technical Manual Chapter 4 Page 2 of 96 2017 Siemens Protection Devices Limited ...
Page 386: ...7SR220 Technical Manual Chapter 4 Page 6 of 96 2017 Siemens Protection Devices Limited ...
Page 398: ...7SR220 Technical Manual Chapter 4 Page 18 of 96 2017 Siemens Protection Devices Limited ...
Page 414: ...7SR220 Technical Manual Chapter 4 Page 34 of 96 2017 Siemens Protection Devices Limited ...
Page 466: ...7SR220 Technical Manual Chapter 4 Page 86 of 96 2017 Siemens Protection Devices Limited ...
Page 468: ...7SR220 Technical Manual Chapter 4 Page 88 of 96 2017 Siemens Protection Devices Limited ...
Page 470: ...7SR220 Technical Manual Chapter 4 Page 90 of 96 2017 Siemens Protection Devices Limited ...
Page 472: ...7SR220 Technical Manual Chapter 4 Page 92 of 96 2017 Siemens Protection Devices Limited ...
Page 643: ...Unrestricted ...